1. Field of the Invention
The present invention relates to a long-reach magnetic detector which is used in a liquid-level gauge system of a large-sized storage tank and well adapted to measurement of the liquid level in the large-sized storage tank.
2. Description of the Prior Art
In a conventional liquid-level gauge system for use in storage tanks provided in oil tankers and petroleum installations, a magnetic detector, which is constructed of a plurality of magnetic sensors arranged in a longitudinal row, is mounted inside a protective pipe which is vertically mounted in the storage tank. When the liquid level in the storage tank varies, a magnet, which is fixedly mounted in a floating member movable up and down along the longitudinal direction of the protective pipe, actuates the magnetic sensors of the magnetic detector to determine a current value of the liquid level in the storage tank which may be a large-sized one reaching a height of several tens of meters.
Such large-sized storage tank requires, naturally, a long-reach magnetic detector.
The conventional long-reach magnetic detectors are classified into the following two types:
(a) A long size type of flexible one which is rolled up in transport (hereinafter referred to as the product "a"); and PA0 (b) A short size type of substantially rigid one, a plurality of which are separate in transport while connected with each other through connectors in installation (hereinafter referred to as the product "b"). PA0 (a) In storage and transport, it is possible to fold the magnetic detector small, which facilitates the handling of the magnetic detector in a safety manner; PA0 (b) In use, the thus folded magnetic detector is transported to the site of a desired installation, in which the detector is stretched or unfolded to assume a long-reach form, which facilitates the installation of the magnetic detector in the liquid-level gauge system; PA0 (c) Since the magnetic sensors of each of the unit elements of the magnetic detector are already connected with each other through the printed boards, band cables and the relay printed boards in the factory, there is no need for connecting these sensors with each other on the installation site at all; and PA0 (d) Since there is no fear that each of the unit elements of the magnetic detector is subjected to large stresses even when the detector is folded, there is substantially no fear that the printed boards and the magnetic sensors are damaged in installation, which ensures the reliability of the the magnetic detector.
As for the product "a", it is widely used in these days. However, the product "a" has its components and and soldered portions subjected to large stresses when rolled up, which arouses troubles and failures in electrical contact areas of the components and the soldered portions of the product "a". Consequently, the product "a" is poor in protection of its components and soldered portions.
As shown in FIG. 8, in another type of the product "a", a plurality of electrical components 22, each of which is housed in a box 21, are mounted on a stainless steel strip 20, wired and embedded in a molded rubber compound 23. This type of the product "a" is costly, and requires a large allowable radius of curvature, which makes the handling of the product "a" difficult in transport.
As for the product "b", it was provided by the applicant's company. However, the product "b" was poor in resistance to corrosion, leading to failures of electrical contacts. When the product "b" was used on marine vessels, many troubles such as disconnection of connectors of the product "b" occurred due to vibrations of the marine vessels.